1. Field of the Invention
The present invention relates to a display apparatus utilizing a light emitting device.
2. Description of the Related Art
An organic electroluminescence (EL) device (which may hereinafter be simply referred to as “device”) as one kind of a light emitting device typically has a constitution in which organic layers 101 are interposed between a reflecting electrode 102 and a transparent electrode 103 on a light extraction side as shown in FIG. 1A. Out of light beams emitted from a light emitting point 201, a light beam 203 to be radiated to a side opposite to the light extraction side as well as a light beam 202 to be radiated to the light extraction side is reflected by the reflecting electrode 102 to the light extraction side, whereby a quantity of light to be extracted through the transparent electrode 103 is increased, and emission efficiency is improved.
However, with such constitution, a light beam 301 incident from an outside of the device is also reflected by the reflecting electrode 102 as shown in FIG. 1B, with the result that a contrast of a display reduces and visibility of the display deteriorates. Reference numeral 303 represents a reflected light beam. This is not a problem inherent in an organic EL display but a problem common to light emitting displays each having a reflective electrode, such as an inorganic EL display and a plasma display.
A method of alleviating such contrast reduction involves utilization of a nature in which a right-hand (left-hand) circularly polarized state of light is reversed to a left-hand (right-hand) circularly polarized state by reflection. For example, Japanese Patent No. 2,761,453 proposes a method involving placing a circularly polarizing plate on a light extraction side to prevent reflection of external light. In addition, Japanese Patent Application Laid-Open No. 2005-332815 proposes a method of preventing reflection of external light with a circularly polarizing plate a polarization degree and transmittance of which are changed depending on a wavelength of light.
Another method involves utilization of interference that is caused in lamination of thin films each having a thickness of about several tens of micrometers to about several hundreds of micrometers for preventing reflection of external light. Japanese Patent No. 3,555,759 proposes a method involving combining interference by an optical resonator and a monochromatic absorption filter, and a method involving combining interference by an optical resonator and a red, green, or blue color filter for each device.
The above constitution of Japanese Patent No. 2,761,453 is simple and is excellent in function of preventing the reflection of external light, but the circularly polarizing plate has a transmittance of about 35 to 45% (the theoretical limit is 50%). As a result, there is a problem that emission efficiencies of organic EL devices are uniformly reduced to half irrespective of luminescent colors of the devices.
In addition, Japanese Patent Application Laid-Open No. 2005-332815 suggests that a polarizing plate showing a high transmittance for a certain wavelength range be commonly applied to light emitting devices showing different luminescent colors. With such constitution, light emitted from a light emitting device showing a luminescent color corresponding to the certain wavelength range can be efficiently extracted. However, the constitution of Japanese Patent Application Laid-Open No. 2005-332815 unnecessarily increases a frequency at which external light is reflected in a light emitting device showing any other luminescent color. That is, the efficiency with which light emitted from a light emitting device showing any other luminescent color is extracted cannot be improved, and the frequency at which external light is reflected increases as compared to that in a case of an ordinary circularly polarizing plate.